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Revoslot Spur Gear Failure

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  • #16

    I am going back to school on plastic design, now that I am 3D printing plastic parts. I am learning that design principles which are good for injection-molded parts aren't necessarily good for printed parts. In point of fact a part well-designed for injection molding can be awful for printing. Especially on a filament printer. And vice-versa.

    For one thing, heavy wall thicknesses aren't a big deal in printed parts, because you can fill much of that thickness with low-density honeycomb. And you can mate up thin walls with thick walls no problem. You don't have to worry about how the plastic will flow, and the possibility of creating sinks and voids. Similarly you can print parts without welds. No issues with weak welds and warpage.

    On the other hand injection-molded parts don't need support structures. They are inherently stronger than printed parts. They come out of the mold with excellent surface finish and usually don't need cleanup. And there are an immense number of plastic resins available for injection-molding that are simply not options for printing.

    I haven't yet gotten involved with liquid resin printing. I'm sure there are a whole different set of design issues to learn about there.

    I just turned 71 years old the other day. This old dog is still busily learning new tricks!

    Ed Bianchi


    • #17
      Originally posted by HO RacePro View Post
      Once upon a time a company would have paid me good money to help them with the design issues of this part. Done it for free here.

      Ed Bianchi
      I'm sure they would be interested in your analysis. I am aware of the issues with flow, temperature, etc. when molding parts. I guess our group has been lucky and is receiving the cream of the crop when it comes to crown gear. It sounds like your beef is you don't think they designed the gear correctly versus the company doesn't stand behind their product. What I would be interested to know is did the seller or the distributor offer replacement parts when you brought this to their attention?


      • #18
        Ed, life starts today, there's nowt wrong with learning new stuff because tomorrow it'll be old stuff.

        I gave up on printing guides and pods, yes I can print both pretty danm good with my resin printer but kudos don't win races, finishing first does.

        Something I realised a while ago with 3DP, WTH are we only printing 3-4 walls and filling with fresh air? It produces weak but lightweight parts...I now only print 4 walls/top/bottom layers then 100% infill, if solid is good for injection molded parts at 10,000psi then it's got to be the only way to go for slowly laying melted squeezed plastic on top of other melted squeezed plastic at atmospheric pressure.

        3DP gears, why would you bother?

        I now print chassis to take SlotIt pods, SlotingPlus guides, NSR/SlotIt gears and my cars run with the NSR/SlotIt guys, yeah I can print all that other stuff just because I can and it's cheaper (is it though?) but my car doesn't end up as quick and I love winning races.
        Last edited by Kevan; 09-25-2021, 07:49 AM.


        • #19

          I too have given up printing guides. The aftermarket injection molded guides available are just far superior to what I can print. I have just ordered some Thunderslot deep-slot guides that look to have the features I crave most -- small, strong, slippery and with set-screws to hold the electricals together. No printed guide I can design can come close.

          But I have my own motor pod designs that I really, really like. Designing them for printing took me in very different directions from the injection molded designs on the market. I use shims to set the sidewinder gear spacing and four 0-80 machine screws to hold the separate axle carrier in place. Said axle carrier is designed to take ball bearings instead of bushings. It all makes for a really light, stiff, compact sidewinder pod that is hugely efficient.

          On top of that I have integrated it into a monocoque design successfully. I have that motor pod as a sub-chassis, a separate guide/front wheel sub-chassis, and a central rattle-pan sub-chassis all held together by the car body. The car is already competitive, and I have further tweaks in process.

          I am not currently using parts that have reduced infill, but there are opportunities there. If you want really light, really stiff parts printing them thick with infill is worth investigating. The stiffness of a part is -- get this -- proportional to the CUBE of its thickness. Make it twice as thick, it becomes EIGHT TIMES as stiff!

          That does not mean it is eight times as STRONG. But very, very stiff -- as in it takes eight times more force to bend it.

          Making thick parts, even if they are light parts, has a noticeable effect on the center of gravity. Also stiff parts don't absorb shocks well. So there are trade-offs.

          But then everything in engineering is a trade-off. Everything!

          Ed Bianchi
          Last edited by HO RacePro; 09-25-2021, 03:36 AM.


          • #20

            You are right. I'm not accusing RevoSlot of failing to stand behind their product. I haven't attempted to return those gears or ask for a refund. I could have. I didn't.

            But I do see design flaws in their gears. If they take notice of my observations and make changes, well, great! And they're welcome. If not, heck. It's not like I work for them.

            Even folks who were paying for my help have been known to ignore my advice. I banked their checks and moved on.

            Ed Bianchi


            • #21
              If RevoSlot would be interested in my advice, here is a simple, inexpensive fix that would get them most of the way home...

              Remove the mold features that produce the oblong cutouts in the gear. That might mean grinding away those features, or replacing mold inserts. That will make the gears stronger and more round without investing in entirely new tooling. Should cost hundreds of dollars, not thousands. The per-part cost will go up a hair because of the little bit of extra plastic in each part. Mold cycle time will probably be unaffected. A cheap and effective fix on total.

              It won't correct the tooth shape so it meshes better with the pinion gear. They'd probably need an entirely new mold to fix that. Not likely, my guess.

              Ed Bianchi


              • #22
                Why not bring out your own gears for this line, with the improvements you cover 'baked in'?

                I'm sure Alan would stock them if they are up to snuff. Everybody wins.....


                • #23
                  While BRM gears are not completely concentric, we find them perfectly serviceable. We break in gears with polish, some use the age old heat trick, also topping the pinion teeth especially on early BRM/ RevoSlot gears.
                  But many of our racers do nothing and cars perform for years, in fact normally pinions wear out way before Spur Gears.
                  As mentioned before happy to replace a Spur that fails in a reasonable time.
                  It is critical to set mesh, break in and reset as high spots on the gear train wear in.
                  This is normal on gearSets, even in Competition Cars, Motorcycles etc.

                  While I agree the gears used are not perfect we just do not see the failures you are talking about. I have 100's of racers using RevoSlot gears without major issues.

                  Even on the heavier BRM Mini cars we are not seeing the issues you experience. Some of my racers have even fitted 30,000 rpm motors and sponge tires so way more load and still no issues here.

                  You do need to break in the gears and yes tweaking gear shape etc are part of the Hobby many enjoy.

                  But trashing RevoSlot is not appreciated here.

                  Tell you what I will gladly do, send me your car and all failed parts and I will refund you.

                  Then you can move on and I can carry on supporting the growth of BRM and RevoSlot.

                  To clarify for anyone else reading this BRM are the Manufacturer of the RevoSlot cars complete running gear.
                  So when I mention BRM and then switch to RevoSlot I hope this clarifies this.

                  Now I need to go get ready I for racing tonight at my Store.
                  I need to replace a gear set in an F1 car to loan out for racing.
                  Not BRM or RevoSlot, but part of the reason and business of racing, wear happens, Heck even on my Competion Motorcycles we see runout on sprockets and tight spots on chains when new. Tires that are not perfectly round and many other issues. Part of setting up, part of the cost effect of manufacturing. It is why aircraft grade bearing are more expensive than wheel bearing for a wheel Barrow or moped.

                  Last edited by Scaleracing; 09-25-2021, 12:01 PM.
                  Alan Smith
                  SCI Owner.



                  • #24

                    I am very sorry you think I am trashing RevoSlot. I happen to like my RevoSlot Toyota Supra. I enjoy racing it. But I have been disappointed in my experiences with the spur gears that I've run on the car. They don't measure up.

                    By contrast I have three Slot.It cars -- also with anglewinder gearing -- that have seen much more track time and have not given me a moment's trouble with the gears. I've actually never touched them. Two of those cars have proven to be very competitive. Someday I might fuss with their gears, but I haven't felt the need to date.

                    In my engineering career I have often run up against folks who got defensive when quality issues arose. That is just part of human nature. At least some human natures. Part of my job was to help people get past their angst while we got on with solving the problem. Solving problems takes time. Often more time than is convenient. The anxiety among the troops had to be managed while we figured out what was going wrong and how to fix it. At times it made things very much harder, and could even move us backwards. It was only when we could demonstrate that we had a fix that worked that the tension resolved itself.

                    Anybody who has ever designed a product knows all too well how difficult it is to get every feature right. Folks who resist making necessary changes do not make good designers. One of the big advancements in modern engineering is the ability to rapidly make and modify prototypes. These days a finished design can have dozens of prototypes and revisions in its history.

                    Most of the issues with the RevoSlot spur gears have a cheap and simple fix, as described above. Why not get it done?

                    Ed Bianchi
                    Last edited by HO RacePro; 09-26-2021, 11:28 AM.


                    • #25
                      Ed please do not talk down to me I have a background in mechanics and engineering too.

                      Including building, and running a sucessful Motorcycle race team.

                      I have also been racing slot cars for over 60 years. So I know what I am doing.

                      I said that BRM gears are not perfect, but they are functional. We see none of the failures you are experiencing. Nor do BRM.

                      Yes the first pinions on RevoSlot cars had incorrectly designed teeth, and topping them certainly improved fit and reduced noise.
                      Yes Spur gears sometime have some run out, and rarely we have seen poorly injected teeth. But your comments make it seem like this is the norm That is not true.

                      I am not BRM but I partner them on the Trans Am cars and work closely with them on racing events uses these exact gears.
                      We have not seen failures even in 24 Hour races.

                      As with everything, except one off production, there will be variations as tooling runs, CNC machines, injection molding also but we honestly have not seen any of the issues you complain about.

                      We sent you 2 gears and you feel that they are not fit for the job of running a RevoSlot Car, send them back, in fact send the car back.

                      I am amazed if your car is so poor yet many have no issues and do not have your engineering knowledge.
                      How they manage to races RevoSlots without the issues you are seeing surprise me.

                      What break in do you do on gears, what lube do you use? I believe you are experiencing issues but it is not the norm.
                      You mentioned not realizing how to change the gear mesh or lash so I was surprised your car ran well at first. These are not Ready to Race cars and anyone who sells them as such is not doing RevoSlot or in fact any Slot Car justice.

                      You need to loctite screws and check the motor mount, bearing fit, axle upright alignment, gear mesh, axle float. Tire fitment and true, set up body float check interior contact with the motor and adjust. Fit the guide for the track you are running on, route wires, line, test break in then check again.

                      Topping gear teeth can create a better mesh, but most of the Racers I know, and very competent racers and builders, do not have issues with these gears especially the Spur. I had never seen a gear break from the hub on a RevoSlot, but obviously it happened to you.

                      You mention, fantastic product but we have seen failed gears there. The car I worked on yesterday was that brand. We race many different brands, and see broken chassis, guides, gears etc but not on any of the brands we support to a level that raises concern.

                      Of course in an ideal World nothing would ever fail, but surely that is not realistic.

                      We know the gears are not perfect but they are normally functional and when not ( rarely happens ) we will gladly replace. That said like tires, motors, lead wires, braid these are all serviceable parts.

                      I just replaced a motor, pinion, braid and guide on a Trans Am car we build in Partnership with BRM. I was amazed that after 3 years of racing including several hard crashes the Spur gear was still perfectly serviceable, So left as is, and last night he won the race.
                      A car using similar gears from BRM, with 3 years service, worn out a motor and guide but still the Spur gear was fine.

                      What you show is not normal I would love to find out why you are having so many issues.

                      Any product I import and sell that fails I will stand behind. Any racing equipment can be modified to perform better that supplied, by Blueprinting, break in and tweaks such as those both you and I have mentioned. But other than careful break in most racers do not find they have to do any of these things to Race RevoSlot, BRM, Scaleauto, etc and enjoy them.

                      Don't get me started on N@# tires though, glad I know longer carry that product But that is another story.

                      Send anything back you feel is not serviceable as supplied and I will gladly service or replace or refund.

                      I stand behind the brands I import 100%
                      Last edited by Scaleracing; 09-26-2021, 10:06 PM.
                      Alan Smith
                      SCI Owner.



                      • #26
                        "and topping them certainly improved fit and reduced noise"
                        "Topping gear teeth"

                        Is there a video somewhere on how to do this?

                        Also what is your recommended method for breaking in the gears?

                        As an aside - I took my large collection of Revoslot to a mate's track yesterday. It was my first chance to give many of them a shake down. I ran them without doing anything to them to see how they went. My MoMo Ferrari 333 was great out of the box and even better once I check gear lash and made sure the wheels or spun freely. With all the rest I check gear lash and make sure the front axle spins freely. That is about all we do and then we race them. I own a large collection of BRM/TTS)and Revoslot cars. I have had one gear issue in all that time. For some mysterious reason the spur gear on my Escort chewed through the teeth. Other than that they have all run well.



                        • #27
                          Hi David,
                          first on the TTS Escort the motor angle is not ideal. Try fitting a BRM center section which has a slightly different angle. It should improve the running of the car.

                          Topping the teeth on the first series RevoSlot pinions is easy.

                          All you are doing is removing the top of the teeth. They are too sharp so bottom in the Spur without being able to control lash. Once a small amount of the top of the tooth is removed the pinion and Spur can mesh better and you will lose lash or rock which hammers the teeth on the Spur, will also run quieter once lash is controlled.

                          This is the only real issue we have here. We fit the later pinions and that will cure the issue, but it can be done to correct the first pinions.
                          If you look at them they are too sharp. Ideally they should have aprox a 1mm removed from the tip of the tooth to prevent bottoming out on the Spur gear.

                          We also sometimes see a little run out or wobble on the Spur, never been an issue here. But I did watch the Italian Race Team at one of our 24 hour races tweek a Spur with pliers bending until the wobble is gone. A bit like truing a bicycle or motorbike spoked wheel.

                          We break in dry or if looking for an even better fit you can polish with tooth paste. Just make sure to wash off when done then lube.

                          You can also use heat to soften the Spur teeth with a bic lighter, as soon as the gear starts to run quieter remove the heat.
                          That is an old trick from the 60's, it works but go slowly if you want to try.

                          Polishing the fit then resetting or even dry break in if in a hurry. Just remember to lube well and clean off any polish or abrasive material or you will wear the gear out instead of bedding them in.

                          Hope this makes sense.
                          Last edited by Scaleracing; 09-26-2021, 10:26 PM.
                          Alan Smith
                          SCI Owner.



                          • #28
                            Two things.

                            First: it’s a darned $4 part. Replace it with an Ergal spur and get on with life. All this ranting and amateur re-engineering is getting stomach churning.
                            My Escort made gear noise that I deemed unacceptable. I bought an Ergal spur and all is well.
                            My 333SP has no gear issue.

                            Second: Alan states “first on the TTS Escort the motor angle is not ideal. Try fitting a BRM center section which has a slightly different angle. It should improve the running of the car.”
                            Does this apply to all Escorts or just a few? Mine is the #16, one of the earlier cars. Is the “center section” referred to BRM S-408E?

                            David Weidler

                            PS: Alan, your PM box is full.


                            • #29
                              Hi David,

                              Sorry for the delay in reply, a lot going on at the Distribution Center and Store these days.

                              The TTS Escort chassis is not ideal angle wise, the BRM version S-408E should give a better match up for the gears.
                              BRM are soon to produce the Escort themselves as they now own the molds. They were the supplier of Chassis and parts, but sadly TTS decided to go it alone which has mean the 2 brands are no longer compatible performance wise.
                              We race the TTS cars here and the Escort is a fun racing car with just the BRM center section change.
                              Hope this helps sorry about the mail box, I get a message when every new member signs up and it overloads my mail box.

                              Best to reach me is
                              Alan Smith
                              SCI Owner.



                              • #30
                                Thanks Alan



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